extract_urbanization_trend

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// released under Open Source GPL License Copyright © 2023 Ka Hei Chow

// ################################# //
// ######    Urbanization     ###### //
// ######     Trends         ###### //
// ################################# //

// this script is used to extract urban areas which are developed adter 2000
// it displays ratio of the newly urbanized grid cells (< 5% is masked out)

// import modules
var palettes = require('users/gena/packages:palettes');
var helper = require('users/pinkychow1010/GEE:WorldBank/helper');
var intraUrban = require('users/pinkychow1010/GEE:WorldBank/app_interface');

// construct app using framework
intraUrban.app(extract_urbanization_trend);

// Karachi
// var bbox = ee.Geometry.Polygon(
//         [[[66.53649977956582, 25.24832952195102],
//           [66.53649977956582, 24.670637047045766],
//           [67.49231032644082, 24.670637047045766],
//           [67.49231032644082, 25.24832952195102]]], null, false);

function extract_urbanization_trend(aoi) {
  
  // import global settlement dataset
  // GHSL: Global Human Settlement Layers, Built-Up Grid
  var bbox = aoi.geometry();
  var GHSL = ee.Image('JRC/GHSL/P2016/BUILT_LDSMT_GLOBE_V1');
  var builtUpMultitemporal = GHSL.select('built').clip(bbox);
  
  // set up data viz
  var palette = palettes.misc.tol_rainbow[7];
  var visParams = {
    min: 0,
    max: 100,
    palette: palette
  };
  
  // get new buildings
  var after2000 = builtUpMultitemporal.eq(3);

  // land use cover by 2021
  var lulc = ee.ImageCollection('ESA/WorldCover/v200')
    .first()
    .clip(bbox);
  
  // get settlements not covered by GHSL
  var urban_mask = lulc.eq(50);
  var no_builtup_2014 = builtUpMultitemporal.eq(2);
  
  // update new settlements
  var newBuilt = urban_mask.and(no_builtup_2014).or(after2000);
  
  // recently urbanization ratio
  var urbanizationRatio = newBuilt.reduceNeighborhood(
      ee.Reducer.mean(), 
      ee.Kernel.circle(600, 'meters')
    ).multiply(100).toByte();
  
  // focus on ubanization clusters
  var threshold = urbanizationRatio.gt(5);
  var masked = urbanizationRatio.updateMask(threshold);
  
  // data visualization
  Map.addLayer(masked, visParams, 'Built-Up Ratio after 2000');
  Map.centerObject(bbox, 10);
  Map.setOptions("HYBRID")
  
  var legend = helper.add_colorbar(visParams, "Urbanization Ratio");
  Map.add(legend);
}